Portman started taking dancing lessons at the age of four. She performed in local troupes, and dreamed of dancing on Broadway. At the age of twelve, Portman was discovered in a pizza parlor by an agent for Revlon, who offered her an opportunity to model. However, she asked to be introduced to acting talent scouts instead of modeling agents. Referring to her discovery in an interview with Blender Magazine, Portman stated "I was definitely different from the other kids. I was more ambitious, I knew what I liked and what I wanted, and I worked very hard. I was a very serious kid."

In July 2001, Portman opened in New York City's Public Theater production of Chekhov's The Seagull, directed by Mike Nichols, playing the role of Nina alongside Meryl Streep, Kevin Kline, and Philip Seymour Hoffman. The play opened at the Delacorte Theater in Central Park. That same year, she was one of many celebrities who made cameo appearances in the comedy Zoolander. Star Wars Episode II: Attack of the Clones was filmed in Sydney during this time, including additional production in London. In 2002, the film opened around the world. Portman was cast in a small role in the film Cold Mountain alongside Jude Law and Nicole Kidman.

In 2004, Portman appeared in the independent movies Garden State and Closer. Garden State was an official selection of the Sundance Film Festival, and won Best First Feature at the Independent Spirit Awards. Her role of Alice in Closer saw Portman win a Supporting Actress Golden Globe as well as a Best Supporting Actress Oscar nomination.

Portman appeared on Saturday Night Live on March 4, 2006, hosting the show with musical guest Fall Out Boy and special guest star Dennis Haysbert. In a now-famous SNL Digital Short, she portrays herself as an angry gangsta rapper (with Andy Samberg as her Flava Flav-esque partner in Viking garb) during a faux-interview with Chris Parnell, saying she cheated at Harvard University while high on pot. The skit is available as an easter egg on the second disc of the 2 disc special edition DVD release of V for Vendetta. In another sketch, she portrays a student named Rebecca Hershlag (her actual surname) attending a Bar Mitzvah, and in an installment of the recurring sketch The Needlers (also known as Sally and Dan, The Couple That Should Be Divorced), plays a fertility specialist (her father's profession).Portman promoting V for Vendetta at Comic Con 2005.